The present invention relates to tubing. More particularly this invention concerns a multilayer tube formed of profiled strip.
A multilayer tube formed of profiled strip is known from German patent document 3,441,064. The strip has inner and outer edges, is formed between them with a double-thickness outwardly directed lip defining an outwardly open inner slot, and is bent back under at its outer edge to form an inwardly open outer slot with the outer edge extending backward toward the inner edge. Where two turns of the strip material overlap, the outwardly directed double-thickness lip of each turn is engaged in the outer slot under the bent-back outer lip of the adjacent turn. Thus the turns are locked together and can shift limitedly relative to each other to allow the tube to be bent. What is more the interfit is so tight that the tube can easily be sealed to safely transport gas or liquid under pressure.
The disadvantage of this system is that, when stretched, relatively wide radially outwardly directed openings are formed that can catch and fill with dirt and the like. Furthermore the tube thus formed is at most two layers thick in many locations so it is not strong. The inner surface of the tube is shingled, with overlapping sections that make flow in the tube turbulent.
It is therefore an object of the present invention to provide an improved tube made of profiled strip.
Another object is the provision of such an improved tube made of profiled strip which overcomes the above-given disadvantages, that is which has smooth outer and inner surfaces even when bent or extended, and which is very strong.
A tube made of profiled strip has according to the invention an inner edge and an outer edge parallel to the inner edge and projecting away from the inner edge. A double-thickness rib extending between the edges projects transversely in a direction from the strip. A channel extending between the rib and the outer edge opens transversely of the strip opposite to the direction in which the rib projects from the strip. The strip is formed into turns centered on an axis with the rib projecting radially outward. The channel opens radially inward, and the rib of each turn projects radially into the channel of an adjacent turn.
Such a tube is therefore made of a uniform-thickness strip of metal that is folded and bent to the desired shape, so it is extremely inexpensive to make and can be made at great speed, in part because the strip can be given its final shape before it is wound up into a tube. The tube seals as tightly as one using substantially more material and the turns are inter-locked such that, even if the tube has an oval or polygonal section, it is very strong while remaining relatively flexible.
According to the invention each outer edge radially outwardly overlies the channel of the adjacent strip and forms therewith a helicoidal compartment along which a seal extends. The channel can form with the rib a pair of helicoidal compartments each holding such an elastomeric seal.
The channel in accordance with the invention is formed with a double-thickness inner lip projecting toward the rib and forming a slot open parallel to the axis toward the rib and inner edge. The outer edge of each turn is axially slidable in the slot of an adjacent turn. The channel can further be formed with a double-thickness inner lip projecting toward the rib and forming a slot open parallel to the axis toward the rib and inner edge. The outer edge radially overlies the lip and the strip further is formed between the outer edge and the rib with an outer lip projecting parallel to the axis and axially slidable in the slot of the adjacent turn.
The strip according to the invention can be formed adjacent the outer edge with an inwardly open groove. A seal extending helicoidally in the groove of each turn radially inwardly engages an adjacent turn between the rib and the outer edge thereof.